Piacenza Experimental Site

The soil treatments from the Piacenza site showed, throughout the experimental period, a similar trend of soil aggregation as for Torino. An overall improvement of soil aggregation was shown for all treatments after the first year (Table 4.4). This was mainly due to greater yield of large aggregate size fractions, as compared to the initial distribution at the onset of experimentation (initial soil). The major effects were achieved for the least disruptive MIN, COM-2, and CAT treatments. Both soil aggregation and stability index were significantly larger than the respective TRA and No-CAT control treatments.

Table 4.4 Piacenza experimental site, percent distribution (%) of water-stable aggregate sizes (mm) and mean-weight diameter index (MWD) (mm) under different treatments for 3 years of experimentation

Treatments

Aggregate size

MWD

4.75-1.00

1.00-0.50

0.50-0.25

<0.25

Control soil

52.8

26.2

9.1

11.9

1.76

Maize

First year

TRA

55.6

21.5

11.0

11.9

1.82

MIN

64.3

17.7

9.1

9.0

2.03

COM-2

63.6

18.3

9.3

8.7

2.01

LSD

5.5

NS

NS

1.7

0.10

Second year

TRA

36.1

33.4

15.6

14.9

1.37

MIN

45.0

27.1

14.7

13.2

1.57

COM-2

45.4

29.5

14.6

10.6

1.59

LSD

3.2

2.4

NS

1.6

0.08

Third year

TRA

53.7

25.9

10.8

9.6

1.79

MIN

50.4

28.1

11.7

9.9

1.72

COM-2

58.8

24.1

9.3

7.8

1.92

LSD

NS

NS

NS

NS

NS

Wheat

First year

CAT

55.1 (0.9)a

23.8 (1.1)

11.2 (0.3)

9.9 (0.3)b

1.82 (0.02)a

No-CAT

49.0 (1.9)b

25.7 (2.7)

10.5 (0.4)

12.5 (1.6)a

1.67 (0.03)b

Second year

CAT

38.4 (0.1)a

29.9 (0.4)b

16.2 (0.5)b

15.5 (0.8)

1.41 (0.03)a

No-CAT

34.6 (1.5)b

30.8 (0.4)a

17.9 (0.8)a

16.7 (1.0)

1.31 (0.04)b

Third year

CAT

47.7 (2.9)

28.2 (1.3)

12.5 (0.6)

11.6(1.4)

1.65 (0.1)

No-CAT

52.5 (5.5)

25.9 (3.0)

11.8 (1.4)

9.8 (1.1)

1.76 (0.1)

LSD least significant difference (n = 4), NS not significant. Different small letters in columns indicate significant difference at 0.05 probability level (n = 4). Numbers in brackets for wheat plots represent standard deviation (n = 4)

LSD least significant difference (n = 4), NS not significant. Different small letters in columns indicate significant difference at 0.05 probability level (n = 4). Numbers in brackets for wheat plots represent standard deviation (n = 4)

A sharp decrease of soil aggregation and stability index occurred in Piacenza for soil treatments under maize after 2 years of field experiments (Table 4.4). All soils showed a breakdown of large size aggregates, and redistribution of soil particles towards smaller size fractions, including microaggregates, though the loss of structural properties was different for various treatments. A persistent effect on soil stability was shown by MIN and COM-2, both characterized by a preservation of water-stable macroaggregates (ffi45%), and a limited reduction in the associated MWD index. Moreover, aggregate fractionation of COM-2 provided the lowest yield of microaggregates (10.6%), whose amount was even smaller than for the initial control soil (11.9%).

For the wheat plots, despite the overall loss of structural properties in the second year, both size-aggregate distribution and MWD index (Table 4.4) indicated that the treatment with biomimetic catalyst preserved soil structural quality more than for the No-CAT treatment.

The positive effect on aggregate stability for the maize field plots under compost was also confirmed at the end of the third experimental year (Table 4.4). With respect to the results of the previous years, the aggregate distribution of TRA, MIN, CAT, and No-CAT indicated an occurred recovery of the original structural stability. The values of aggregate yields and stability index for these treatments reached those found at the onset of experiments, thereby suggesting a progressive lower efficacy of both MIN and CAT on soil structural quality. Conversely, COM-2 plots showed a continuous decrease of both microaggregates (—2.8%) and intermediate macroaggregate fractions, which became firmly incorporated into larger sized aggregates (+13.4%), thus improving the overall soil structural stability index (1.92).

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